This invention relates to a fuel supply system and method for a direct fuel injection type internal combustion engine in which is directly injected into a combustion chamber of the engine. It particularly relates to a fuel supply system and method for the engine of the spark ignition system useful as an automobile gasoline engine or the like.
In this kind of the engines with the spark ignition system, fuel (gasoline fuel) is directly injected into a combustion chamber of each cylinder by each injector. In order to assure a predetermined fuel pressure required for the direct fuel injection engine, the fuel to be supplied into the combustion chamber is pressured with a high-pressure fuel pump. The high-pressure fuel pump is connected with the camshaft which serves to drive intake and exhaust valves, and driven by a rotation power of the camshaft. The fuel pressurized by the high-pressure fuel pump is fed to the injector (for example, JP-A-04-393152).
In case of using the camshaft as a power source for the high-pressure fuel pump, the high-pressure fuel pump cannot be driven at a required speed during cranking at the time of a start-up of the engine, because the revolution speed of a crankshaft during cranking is low, and the revolution speed of the camshaft is also low accordingly. As a consequence, the pressure of fuel to be supplied to the injector cannot be brought to a fuel pressure required at the time of a start-up of the engine.
Accordingly, fuel cannot be injected into the combustion chamber under any sufficient fuel pressure during cranking of the engine. This results in insufficient atomization of fuel mist, and hence, coarse droplets of fuel as a liquid film adhere on a wall surface of each combustion chamber, so that a large amount of the fuel adhered as the liquid film is emitted as unburned fuel (HC) from the combustion chamber. During a self-sustaining operation after full expansion, the fuel adhered as the liquid film tends to be emitted as HC when the internal combustion engine is under cold engine conditions (under cold conditions). These cause deterioration in the emission performance of the internal combustion engine.
Examples of fuel supply systems for spark ignition engines of the direct fuel injection type, which have been developed to overcome this problem, is equipped with a high-pressure fuel pump connected with the camshaft of an internal combustion engine via a speed-increasing and variable speed device (for example, JP-A-10-009074).
In this fuel supply system, an actuator of the variable speed device is operated on the basis of a detection signal from a starter switch of the internal combustion engine, a fuel pressure sensor, a crank angle sensor or the like such that the variable speed device is changed over to a speed-increasing side to rotate the high-pressure fuel pump at a higher speed and thus, to pressurize the pressure of fuel. When the fuel pressure rises to a predetermined value or greater, and the start-up of the internal combustion engine is recognized to have completed by a start-up completion recognition means, the actuator is then operated to change over the variable speed device to a constant speed side such that the number of revolutions of the high-pressure fuel pump becomes consistent with that of the camshaft.
There are also some fuel supply systems in which by using force produced by an action of an driver prior to a start-up of an engine, an auxiliary start-up pump which is different from a high-pressure fuel pump is mechanically operated to pressurize beforehand fuel to be injected (for example, JP-A-11-132124).
With a fuel supply system such as that disclosed in JP-A-10-009074, the time required until the pressure of fuel reaches a predetermined value can be shortened compared with the conventional driving system without any variable speed device. Where the fuel pressure required during cranking is very high, for example, as high as 10 MPa or higher to increase the number of revolutions of the high-pressure fuel pump in interlocking with a starter switch of the internal combustion engine, however, the pressure of fuel from a turn-on of the starter switch until a first injection of fuel can hardly be raised to a target value in a short time. Moreover, the configuration of the high-pressure fuel pump including the variable speed device is accompanied by a problem that it is complex and requires high cost.
In a fuel supply system such as that disclosed in JP-A-11132124, it is considered possible to have the fuel pressure sufficiently reached a required value at the time of cranking. Due to a limitation on power to be generated based on an action of driver prior to a start-up of the engine, a limitation is imposed on the time during which the fuel pressure can be maintained at the required value. It is thus difficult to prevent fuel from adhering as a liquid film, which is a cause of HC emission, on the wall surface of each combustion chamber in the self-sustaining operation range after full expansion.